1. Field of the Invention
This invention relates generally to conveyor systems principally used in the mining and material handling industry, and more particularly to the design of conveyor loading zones, conveyor impact beds often referred to as an “impact saddle” often used to support a conveyor belt at a point where soil, rocks, gravel and other material drop onto a conveyor belt.
2. Discussion of the Prior Art
In the mining industries, conveyor systems are often used to move bulk material comprising dirt, ore, coal, tailings, etc. from one point to another. The bulk material may be dropped on to the moving conveyor belt from the bucket of a large power shovel or from the box of a dump truck from a considerable height above the level of the conveyor belt. Where the material to be conveyed includes heavy rocks and even boulders or the like, the impact of such objects striking the conveyor can rapidly damage a conveyor belt unless it is adequately supported from below.
To address this problem, conveyor system manufacturers produce and sell impact saddles to be used in heavy impact areas in which idler rollers are mounted in a frame so as to be rotatable by the friction drag imparted by the underside of the conveyor belt which the impact saddle supports.
When transporting loose materials, such as sand, gravel, dirt and rocks, the conveyor belt preferably has a concave curvature and, hence, the rollers comprising the impact saddle include a roller mounted on a horizontal axis and two side rollers that are inclined to the axis of the bottom roller. This configuration necessarily causes pinch points between the inclined rollers and the horizontal one. Such pinch points often result in premature belt failure.
Other known prior art impact cradles consist of a plurality of impact bars bolted to a framework which support a conveyor belt in generally the same shape as the conveyor idlers on the conveyor. The impact bars usually consist of extruded aluminum or formed steel “T” channels molded into a rubber or polymer impact absorbing material having a UHMWPE or Teflon upper sliding surface on which the conveyor slides. “T” bolts or other types of threaded fasteners are inserted into the “T” channel to fasten the bar to the underlying conveyor structure. A typical impact cradle of this type is shown in Andersson, U.S. Pat. No. 4,793,470 issued Dec. 27, 1988.
Other impact/slider bars may have no internal metal “T” slot and may be manufactured of a 100% polymer material, but still utilize a “T” slot molded into the bar in which a fastener is inserted to attach to the bar to the underlying conveyor structure. Some other systems are attached by drilling a hole through the impact bar and fastening the bar to the underlying conveyor structure with a countersunk bolt or fastener and then plugging the surface of the hole with a UHMW cap or another polymer material.
The problem with attaching impact bars with fasteners, nuts, bolts, etc., is that they are labor intensive to install and maintain, they can vibrate loose, rust or corrode and removing them often takes a cutting torch which can result in fires and added expense. Also, when there is internal metal in an impact/slider bar, if a conveyor wears through the polymeric sliding surface, metal may be exposed which may cause wear or grooving of the underside of the conveyor belt. Prior art impact and slider bars with internal metal are also more expensive to manufacture as more steps are needed to bond the metal to the polymer and metal add to the cost. Impact bars without metal are easier to recycle and less costly to dispose of. With many governmental agencies requiring separating of different types of materials that have to be disposed of for recycling or proper disposal, the present invention can provide substantial cost savings over many of the prior art systems.
Another type of impact cradle is shown in the Stoll/Richwood Industries U.S. Pat. No. 5,038,924, issued Aug. 13, 1991. Richwood uses a fastenerless system in which support frames, mounted in a transverse relation to the conveyor belt, are designed to support polymeric segments that are threaded onto the frames to support the conveyor and act as a wear and impact surface. This system has advantages over some of the prior art as it eliminates the use of many of the troublesome fasteners, but it still has shortcomings in that it is not easy to inspect worn segments, is not easily adjustable for wear or is not easily adaptable to many of the low profile or specially designed conveyor systems (e.g. underground coal mining tailpiece loading stations) in the conveyor and material handling industry. The segments are also sometimes difficult to slide on as the friction between the often heavy belt, the segments and the mounting frame has to be overcome when threading the segments onto the frame.